Phoebus Question

[Rebecca Harding - STFC UKRI via Tech-talk <tech-talk at aps.anl.gov>]

Hello TechTalk,

 

There’s something I’d like to do with EPICS and Phoebus, and I don’t know of a good way to do it, so I thought I’d ask here.

 

I’m writing an IOC for a capacitor bank system. I have a simple ao record that represents the target voltage, and I have another record that represents the charging voltage, which is waveform record.

 

I want the target voltage to be displayed as a line on a graph, next to the charging voltage, so the user can compare their target voltage and charging voltage. See attached image for what I’d like the result to look like.

 

[Note that I’m just running a very basic simulation of the capacitor bank at the moment, so that’s why my charging voltage is linear instead of logarithmic.]

 

 

Anyway, at the moment, I’ve got an XY Plot for charging voltage and got a Data Browser looking at target voltage (occupying the same space so that it looks like one graph). This is not ideal because I don’t care about any previous values of target voltage – I don’t really want to see the value over time, I just want the present value plotted as a line. Second image shows the problem.

 

There is another workaround I thought of, which is to just create another waveform record and fill up all its elements with the present target voltage value. That way, I’d then be able to show that as a second trace on my XY Plot. But this solution isn’t ideal either as I feel I shouldn’t have to add another record to my database in order to do what I want in the UI.

 

So, I wanted to ask, has anyone else ever had the desired to show a single scalar value as a line on a graph, and if so, how did you achieve this?

 

Kind regards,

 

Rebecca Harding (she/her)

Controls Software Engineer

Central Laser Facility

Science and Technology Facilities Council

rebecca.harding at stfc.ac.uk